Title page for ETD etd-12152010-225246

Insights Into the Stratigraphic Evolution of the Early Pennsylvanian Pocahontas Basin, Virginia

Degree

PhD

Department

Geosciences

Advisory Committee

Advisor Name

Title

Eriksson, Kenneth A.

Committee Chair

Greb, Stephen F.

Committee Member

Henika, William S.

Committee Member

Kowalewski, Michal

Committee Member

Read, James Fredrick

Committee Member

Keywords

Sequence Stratigraphy

Seal Evaluation

Appalachian Basin

Facies Analysis

Pennsylvanian

Alleghanian Orogeny

Date of Defense

2010-12-08

Availability

restricted

Abstract

Early Pennsylvanian, coal-bearing, siliciclastic strata of the Breathitt Group within the Pocahontas Basin, southwestern Virginia, define a southeasterly thickening clastic wedge deposited in continental to marginal marine environments influenced by recurring, high-magnitude relative sea-level fluctuations and low-frequency changes in tectonic loading. A robust dataset of >1200 well logs, cores and numerous outcrops allowed a unique review of the Central Appalachian lithologic record during both the Late Paleozoic Ice Age and onset of the Alleghanian Orogeny.

The tropical depositional landscape produced stacked deposits of braided-fluvial channels, broad alluvial plains, tidally-influenced estuaries and small deltas. Trends in facies associations allowed development of a high-resolution sequence stratigraphic architecture based on regional flooding surfaces and bounding discontinuities. Analysis of vertical stacking patterns of lithofacies on regional cross-sections identified 15 widespread, unconformity-bounded depositional sequences with an average duration of ~80 kyr based on available geochronology.

Glacioeustatic control on stratigraphic architecture is supported by corresponding sequence duration within the short-eccentricity periodicity of the Milankovitch band, as well as the magnitude and extent of rapid facies shifts, suggesting that far-a-field variations in overall Gondwanan ice-sheet size and volume impacted base-level changes in the tropical basin. The progressive increase in magnitude of transgressions, as indicated by brackish-marine ichnofacies and other faunal indicators within regional high-frequency transgressive system tracts, indicate extrabasinal trends in ice-volume and eustasy.

Petrology and detrital-zircon geochronology indicates that sediment was derived from low-grade metamorphic Grenvillian-Avalonian terranes and recycling of older Paleozoic sedimentary rocks uplifted as part of the Alleghanian orogen towards the southeast and, in part, from the Archean Superior Province to the north.